The present invention relates to changing devices. More particularly, it relates to a changing device for a machine for simultaneous pulling of several threads which run parallel to one another.
Changing units for spooling of threads beads for example 6,000 m/min are known. In these changing units the threads are guided reciprocatingly by blades which are arranged as propellers on two rotors rotatable opposite to one another with constant rotary speeds. The alternating movement of the threads is actuated therefore not as in the conventional changing units by a single reciprocatingly movable thread guide, but instead by blades movable in opposite directions in two adjacent planes so as to alternatingly engage and guide the threads. The transfer of the thread from one blade of another rotor is performed by eccentric arrangement of the shaft of one rotor relative to the shaft of the other rotor and/or by additional stationary thread guiding elements, such as for example a thread guiding ruler. The changing is performed without reciprocatingly moved machine parts.
One of such changing devices, of which the changing device of the present invention is a further important improvement and modification, is disclosed in the German document DE-OS 33 07 915, FIG. 9. This changing device is used for a machine with simultaneous spooling of several threads which run parallel to one another. In correspondence with the number of the threads the changing device has several blade changing units which are arranged in a row so that the blades of the first rotors of all changing units are located jointly in a single first plane, while the blades of the second rotors of all changing units are located in a single second plane.
The blades of the adjacent changing units rotate in opposite directions both in the first plane and in the second plane. With a respective phase position, the rotary circles can overlap so that the blades do not strike one another or do not hinder the opposite position. The overlapping of the rotary circles is positively provided by the requirement that the intermediate spaces between the changing strokes of the adjacent changing units are to be maintained very small. The spool sleeves on which the threads are wound can be clamped on a single long spool spindle, so that they are located at their end sides close to one another.
In the known arrangement the drive of the first rotors and the drive of the second rotors is formed as flat multi-shaft drive. A drive belt provided with teeth on its both sides engages with a toothed drive pulley and surrounds the toothed pulley of the first rotors of the adjacent changing units. Another drive belt engaging with a toothed drive pulley surrounds the toothed pulley of the second rotors of the adjacent changing units at alternating side.
The length of the drive belts can deviate from their nominal value because of manufacturing tolerances, aging process, pulling tension produced during operation, and temperature fluctuations. In the case of a belt transmission such deviations lead to phase errors of the rotors. The greater is the length between the driving pulley and the driven pulley the greater can be the phase error. The deviations can have different magnitudes in different belts and can be subjected to uncontrollable changes. In the known arrangement, due to different length variations of both drive belts in the rotors, the changing units located the farthest from the driving pulley can obtain phase differences of several degrees. Such differences lead to disturbances in laying of threads.
The European patent document EP-B1-0 194 648 deals especially with the problem of providing a play-free exact phase length of the blade, for avoiding the undesired disturbances of the thread laying. This reference discloses a changing unit in which the first rotor is driven from an inner toothing of the second rotor through a transmission shaft. This shaft as well as the shaft of the first rotor is supported in an eccentric bushing which is displaceable relative to the housing. By turning the eccentric bushings relative to one another, the transmission unit during mounting of the transmission can be adjusted so that no tooth gaps are provided. Then the blades are mounted on the base body so that they occupy exactly fixed positions. This construction is extremely complicated and expensive.